Molecular biology of positive strand RNA viruses

Category Archives: Bees

We are conducting a trial of coordinated Varroa treatment in conjunction with the beekeepers on the Isle of Arran. In late September DJE and Luke Woodford – the EastBIO-funded student leading the project – visited Arran to present an evening lecture on Varroa and DWV: Science and Practical Beekeeping.

Our studies exploit our understanding of changes in the virus population associated with Varroa transmission (rather than transmission from bee to bee during feeding) to monitor the ‘health’ of the colony.

The talk was followed by an extended question and answer session covering the project and more general aspects of beekeeping and Varroa control.

The Isle of Arran was looking fantastic as we crossed from Ardrossan on the CalMac ferry. Goatfell, the highest point on the Arran horseshoe ridge (see image above) is a great walk and thoroughly recommended.

One of our colonies in the bee shed swarmed last week. The swarm ended up clustering around the entrance to the hive it had ‘escaped’ from. It was captured and rehoused successfully. The swarm in the picture is up to 5cm deep in places and probably contains 10-15,000 worker bees … and a single queen bee.

Swarmtastic!

Swarming is the natural way that a honey bee colony ‘reproduces’. The old queen and all of the older foragers leave the hive to establish a new colony. The remaining workers raise a new queen from an egg or young larva in the original hive, so generating two colonies from one. Swarming usually occurs in late Spring or early Summer.

Our snappily-titled manuscript “The Iflaviruses Sacbrood virus and Deformed wing virus evoke different transcriptional responses in the honeybee which may facilitate their horizontal or vertical transmission” has just been published in PeerJ. We analysed changes in the transcriptome following infection with deformed wing virus (DWV) and sacbrood virus, or DWV alone. We propose that the difference in expression we observed of the honeybee immune genes induced by SBV and DWV may be an evolutionary adaptation to the different predominant transmission routes used by these viruses .

On Thursday 14th January I’m talking at an evening meeting of Fife Beekeepers Association about the biology of Deformed Wing Virus and how our understanding of the virus should help devise more rational integrated pest management strategies. This is the first of several outreach events planned for 2016 in which our BBSRC-funded research on honeybee viruses will be discussed.

Not long now until the beekeeping season starts and we can get on with our planned field studies 🙂

During previous research on deformed wing virus (DWV) biology and its transmission by Varroa I’ve moved known Varroa-free colonies (sourced from a region of the UK which the mite has yet to reach and maintained totally mite-free) into apiaries in the countryside. Within 2-3 weeks Varroa was detectable in sealed brood, showing that mite infestation occurs very readily. I know other researchers who have made very similar observations. Where do these mites come from?

They’re not all ‘your’ bees

The obvious source would be the phoretic mites transported on workers ‘drifting’ from nearby infested colonies, or on drones which are known to travel quite long distances and may be accepted by almost any colony. If you want to see how frequent this is try marking a few dozen drones with a dab of paint. To avoid confusion use the colour used to mark queens next year. There are unlikely to be 4+ year old queens in the apiary and the drones will all perish before the end of the current season. Over the next few days and weeks the drones will appear in adjacent colonies, and some will likely leave the apiary and be accepted in your neighbours colonies.

Hives in rows …

Beekeepers are usually aware that colonies at the ends of rows often ‘accumulate’ bees that have drifted when returning to the hive. In shared association apiaries some crafty beekeepers will site their colonies at the ends of rows to take advantage of the ‘generosity’ of other colonies. However, many beekeepers probably do not appreciate the extent to which drifting occurs. Pfeiffer and Crailsheim report (1998) that 13-42% of the population of a colony are ‘alien’ i.e. have drifted from adjacent hives, depending upon the time of season. Remember that drifting occurs in both directions simultaneously, so the overall numbers of bees in a colony may not be adversely affected (or boosted). In other studies Sekulja and colleagues report (2014) that ~1% of marked bees drifted between colonies over a three day observation window. Interestingly, American foulbrood (AFB) infected bees drifted slightly more than uninfected bees. Spread of foulbroods during drifting is one reason the bee inspectors check nearby apiaries when there is an outbreak. These studies were all on workers where drifting primarily occurs during orientation flights before the bees become foragers. Drones drift two to three times more than workers (Free, 1958).

The likelihood of drifting must be closely related to the separation of hives and apiaries. Although workers will forage up to 2-3 miles from the hive I suspect the proportion of bees that drift this distance is small to undetectable. Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies. I’ve regularly found drones appearing in (relatively) isolated mini-nucs. I’m not aware of studies that have formally tested drifting between apiaries (though it is reported in passing in the Sekulja et al., 2014 paper referenced above).

Consequences of drifting

So, your hives contain workers and drones from many nearby colonies, and you can only really be sure that they’re all “your” bees if you live – as the sole beekeeper – on an isolated island. Not only does your neighbour generously exchange bees with you, he or she also kindly shares the phoretic mites those bees are carrying, the viral payload the bees and mites are infected with and – if you’re really unlucky – the Paenibacillus larvae spores responsible for causing AFB infection (and vice versa of course).

There are lessons here that should inform the way we conduct our integrated pest management to maintain healthy colonies.

This post provides background information for an article (“Viruses and Varroa: Using our current controls more effectively” by David Evans, Fiona Highet and Alan Bowman) in the December 2015 issue of Scottish Beekeeper, the monthly magazine for members of the Scottish Beekeepers Association.

I enjoyed speaking at the Scottish Beekeepers November meeting in Perth last Saturday. This was the first of several specifically Scottish outreach-type events I’m doing over the next few months and it was a great opportunity to meet people I’ve corresponded with online – often via the highly informative SBAi forum – or who my research group are already collaborating with.

I’m delighted to be talking at the Hampshire Beekeepers Association autumn convention at Sparsholt College this weekend. This is the first of several ‘winter talks’ to BKAs about our research on deformed wing virus and Varroa. Time permitting I hope to discuss some forthcoming studies on coordinated Varroa control that we’re doing with Alan Bowman (Aberdeen) and Fiona Highet (SASA) and that will shortly be featured in the Scottish Beekeeper. I was invited to talk at this event before accepting a post in St. Andrews … it’s a long way to travel. However, one of the advantages of flying to these events is I can’t be tempted by too many goodies from the trade stands 😉

Late last week, in the dark and rain, the first two honeybee colonies were installed in the bee house on our research apiary. The warm(ish) and dry environment will greatly benefit our research by helping us harvest larvae and pupae whatever the weather conditions are outside. In addition, we expect brood rearing by the colony to be extended earlier and later in the season, so enabling us to undertake more extensive studies of the biology of deformed wing virus.

The bee shed has special windows – just about visible in the poor quality cellphone picture – that allows the bees that leave the hive when the roof is removed to ‘escape’ from the shed … they can then re-enter the hive via a tunnel entrance through the shed wall.